1. Field of Invention
The present invention relates to ballasts with inverters having series-tuned L-C output circuitry by which to provide a magnitude-controllable sinusoidal output voltage to a lamp load.
2. Elements of Prior Art
In inverter-type fluorescent lamp ballasts using a series-excited parallel-loaded resonant L-C circuit for matching the inverter's output to the fluorescent lamp, an important problem relates to possible damage of the inverter in case the series-excited parallel-loaded resonant L-C circuit is left unloaded, such as may occur if the fluorescent lamp were to be removed. To prevent such damage from occurring, it is necessary to provide means whereby the maximum power drawn from the inverter be manifestly limited to a safe level.
For instance, such limitation is accomplished by Zansky in U.S. Pat. No. 4,392,087 by using the inverter's DC supply as an alternative load which, by way of rectifier means, activates as soon as the output voltage exceeds a certain magnitude. Or, in U.S. Pat. No. 4,398,126 to Zuchtriegel, inverter protection is provided by way of disabling the inverter in case the L-C circuit is left unloaded.